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~) <br />1'IIiPWOIYI'li-PAWLAK GL•'O'flCIiNICAL, INC. snznaoad 154 <br />Glcnwoai Spnnr,.., CO rilGrll <br />December 2, 1994 14,a 31u 9.15~Y•LSl <br />I'Lunc ;103 94.5-TJX4 <br />NCIG Financial, Inc. <br />Attn: Peter Mattheis <br />0364 Stontt King Road <br />New Castle, Colorado 81647 Job No. 194 543 <br />Sulijccl: Continents Regarding Stability of Graded Cut and Pill Slopes, New Castle <br />Energy Minc Facilities, County Road 335, Gazfield County, Colorado. <br />Gentlemen: <br />As requested, we have reviewed the geotcchnical reports and gmding plan prepared for the <br />subject site and made a cursory review of the constructed grading conditions. The <br />purpose of our work was to develop opinions on llte overall stability of tltc graded slopes. <br />Our review does not include Uie portal slopes. <br />Previous Studies: We were provided a geotechnical.report prepared for grading design <br />and processing facilities by Clten & Associates (Chen, 1985). The grading plan was <br />prepared by Schmueser & Associates. A reproduction of Ute grading plan presented in <br />Chen's report is attached. <br />Subsoil Conditions: The subsoils encountered in the development azea by Clten's borings <br />consist mainly of gravelly sand acrd clay. Soils of higher gravel content and less clay were <br />also found. No free water was encountcrd to the drilled depths of 15 to 70 feet and the <br />Itatural moisture was relatively low. <br />Site Grading: We have not been provided an as-build grading plan. It appears from our <br />cursory observations of Ute site Utat the grading was generally conducted according to <br />Sclmtuese~s grading design. The design cut and £Il slopes range to a ntaxintunt lteigltt of <br />25 feet and maximum grade of 13/4:1 (horizontal to vertical) according to the Chen <br />report. T(te on-site soils were used to construct the fill embankments. <br />Slope Stability: We did not observe indications of overall instability of the constructed <br />slopes. The soil conditions identif ed by Chen & Associates appear appropriate for the <br />stability analysis. Accordingly, we have assumed Ute following pazanieters: <br />Internal Friction: <br />32° <br />Cohesion: 200 psf <br />Moist Unit Weight: 125 pcf <br />Maximum Slope Height: 25 feet <br />Maximum Slope Grade: 30° (1 3/4:1) <br />Fully drained embanklnent and foundation <br />We understand Utat graded slopes sleeper than 2:1 require a safety factor of at least 1.3. <br />Based on the assigned subsoil and gradins parameters, the calculated safety factor against <br />~~ <br />